Construction machine

ABSTRACT

An object of the present invention is to provide a construction machine that can reduce particulate matter (PM) or nitrogen oxide (NOx) discharged from an internal combustion engine mounted on the construction machine. 
     The construction machine  200  includes a diesel engine  101  controlled based on a torque command, an electric motor  102  mechanically connected to the diesel engine, an electric energy storage device  111  that supplies electric power to the electric motor, and a hydraulic pump  103 . The construction machine performs work by driving the hydraulic pump using the diesel engine and the electric motor. A speed control device  118  controls a speed of the electric motor  102  based on a speed command. A torque limiter  115  obtains the torque command having a rate of change with time limited based on a torque target.

TECHNICAL FIELD

The present invention relates generally to construction machines and,more particularly, to a construction machine that performs workhydraulically by driving a hydraulic pressure generator with an internalcombustion engine and an electric motor.

BACKGROUND ART

A known technique in a hybrid construction machine accurately brings anengine to a target operating state by causing a motor generator toassist the engine or to generate electricity through an as simple aspossible configuration (see, for example, patent document 1). To achievethat task, the technique disclosed in patent document 1 incorporates acontroller that obtains an engine speed corresponding to optimum torqueof a set speed as a target speed and performs the following control soas to bring the engine close to an optimum operating state.Specifically, when the engine speed is lower than the target speedbecause of a large load torque on the engine, the controller causes themotor generator to operate as an electric motor according to adifference therebetween to thereby assist torque. When the engine speedis higher than the target speed because of a small load torque on theengine, the controller causes the motor generator to operate as agenerator according to the difference therebetween to thereby store thegenerated electricity in a battery.

Another known control technique is, even with a sharp increase in ahydraulic load, to increase driving power supplied to a hydraulicpressure generator in response to the increase in the hydraulic load,while maintaining appropriate operating conditions of an internalcombustion engine (see, for example, patent document 2). To achieve thattask, the technique disclosed in patent document 2, while causing theinternal combustion engine to drive the hydraulic pressure generator,sets a rate of increase in an output of the internal combustion engineto a predetermined value. An output upper limit value of the internalcombustion engine obtained from the predetermined value of the rate ofincrease is then compared with a driving power requirement obtained froma hydraulic pressure output that the hydraulic pressure generator isrequired to produce. The output of the internal combustion engine isthen controlled so as to be equal to, or smaller than, the output upperlimit value when the driving power requirement exceeds the output upperlimit value.

PRIOR ART DOCUMENTS Patent Documents

Patent Document 1: JP-2003-28071-A

Patent Document 2: JP-2009-216058-A

SUMMARY OF THE INVENTION Problem to be Solved by the Invention

The technique disclosed in patent document 1 does not, however, considera transient state when the load torque undergoes a sudden change andthus involves an unavoidable situation in which a rate of change withtime in the output torque of the engine as an internal combustion enginebecomes high. This requires excessive fuel injection and may produce alarge amount of particulate matter (PM) or nitrogen oxide (NOx).

The technique disclosed in patent document 2 controls an electric motorbased on the output requirement of the hydraulic pressure generator andthus requires the output requirement of the hydraulic pressuregenerator. With construction machines, however, it is difficult toidentify a load on a work implement, to detect a flow rate of hydraulicfluid in detail, and thus to accurately detect or estimate the outputrequirement. Moreover, because the electric motor is controlled withouthaving feedback information on states of the engine, an error involvedwith the output requirement hampers accurate control of the rate ofchange with time in the engine output torque. For these reasons, a largeamount of particulate matter (PM) or nitrogen oxide (NOx) may beproduced, as with patent document 1.

An object of the present invention is to provide a construction machinethat can reduce particulate matter (PM) or nitrogen oxide (NOx)discharged from an internal combustion engine mounted on theconstruction machine.

Means for Solving the Problem

To achieve the foregoing object, the present invention provides aconstruction machine including an internal combustion engine controlledbased on a torque command, an electric motor mechanically connected tothe internal combustion engine and an electric energy storage devicethat supplies electric power to the electric motorgenerator. Theconstruction machine performs work by driving a hydraulic pressuregenerator using the internal combustion engine and the electric motor.The construction machine includes: first control means that controls aspeed of the electric motor based on a speed command; and second controlmeans that obtains the torque command having a rate of change with timelimited based on a torque target.

The present invention further provides a construction machine includingan internal combustion engine, an electric motor mechanically connectedto the internal combustion engine and an electric energy storage devicethat supplies electric power to the electric motor. The constructionmachine performs work by driving a hydraulic pressure generator usingthe internal combustion engine and the electric motor. The electricmotor is speed-controlled by a speed command, and torque of the internalcombustion engine is greater than torque of the electric motor when arate of change with time in torque of the hydraulic pressure generatoris low, and the torque of the electric motor is greater than the torqueof the internal combustion engine when the rate of change with time inthe torque of the hydraulic pressure generator is high.

The present invention still further provides a construction machineincluding: an internal combustion engine; an electric motor mechanicallyconnected to the internal combustion engine; an electric energy storagedevice that supplies electric power to the electric motor; and ahydraulic pressure generator. The construction machine performs work bydriving the hydraulic pressure generator using the internal combustionengine and the electric motor. The electric motor is speed-controlled bythe speed command, and a change of a rate of change with time in torqueof the internal combustion engine is higher than a change of a rate ofchange with time in torque of the hydraulic pressure generator when therate of change with time in the torque of the hydraulic pressuregenerator is low, and the change of the rate of change with time in thetorque of the internal combustion engine is lower than the change of therate of change with time in the torque of the hydraulic pressuregenerator when the rate of change with time in the torque of thehydraulic pressure generator is high.

Such arrangements allow the particulate matter (PM) or the nitrogenoxide (NOx) discharged from the internal combustion engine mounted onthe construction machine to be reduced.

Effect of the Invention

The present invention can reduce the particulate matter (PM) or thenitrogen oxide (NOx) discharged from the internal combustion enginemounted on the construction machine.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view showing a general arrangement of a constructionmachine according to a first embodiment of the present invention.

FIG. 2 is a block diagram showing an arrangement of a drive system thatdrives the construction machine according to the first embodiment of thepresent invention.

FIG. 3 is a set of timing charts showing operations of the drive systemincorporated in the construction machine according to the firstembodiment of the present invention.

FIG. 4 is a set of timing charts showing operations of the drive systemincorporated in the construction machine according to the firstembodiment of the present invention.

FIG. 5 is a set of timing charts showing operations of the drive systemincorporated in the construction machine according to the firstembodiment of the present invention.

FIG. 6 is a set of timing charts showing operations of the drive systemincorporated in the construction machine according to the firstembodiment of the present invention.

FIG. 7 is a set of timing charts showing operations of the drive systemincorporated in the construction machine according to the firstembodiment of the present invention.

FIG. 8 is a set of timing charts showing operations of the drive systemincorporated in the construction machine according to the firstembodiment of the present invention.

FIG. 9 is a block diagram showing an arrangement of a drive system thatdrives a construction machine according to a second embodiment of thepresent invention.

FIG. 10 is a set of timing charts showing operations of the drive systemincorporated in the construction machine according to the secondembodiment of the present invention.

FIG. 11 is a set of timing charts showing operations of the drive systemincorporated in the construction machine according to the secondembodiment of the present invention.

MODES FOR CARRYING OUT THE INVENTION

Arrangements and operations of a construction machine according to afirst embodiment of the present invention will be described below withreference to FIGS. 1 to 8. The following description assumes that theconstruction machine is a hydraulic excavator as a representativeconstruction machine.

A general arrangement of the construction machine according to the firstembodiment of the present invention will be described with reference toFIG. 1.

FIG. 1 is a side view showing the general arrangement of theconstruction machine according to the first embodiment of the presentinvention.

A hydraulic excavator 200 includes a track structure 201 and a swingstructure 202. The track structure 201 has a function of causing theconstruction machine to travel with a track hydraulic motor. The trackstructure includes a right track structure and a left track structure,each being driven by an independent track hydraulic motor. The swingstructure 202 is rotated relative to the track structure 201 by a swingmechanism 113.

The swing structure 202 includes a boom 203, an arm 204, and a bucket205 that perform excavating work, the boom 203, the arm 204, and thebucket 205 being disposed on the other side (e.g., on the right-handside, looking to the front) at a front portion of the swing structure202. The boom 203, the arm 204, and the bucket 205 are driven by ahydraulic cylinder 107, a hydraulic cylinder 106, and a hydrauliccylinder 105, respectively.

The swing structure 202 further includes a cab 206. An operator gets onboard the cab 206 and uses an operating lever to operate theconstruction machine 200.

An arrangement of a drive system that drives the construction machineaccording to the first embodiment will be described below with referenceto FIG. 2.

FIG. 2 is a block diagram showing the arrangement of the drive systemthat drives the construction machine according to the first embodimentof the present invention.

A diesel engine 101 as an internal combustion engine and a firstelectric motor 102 are mechanically connected to each other to therebydrive a hydraulic pump 103 as a hydraulic pressure generator. It is herenoted that, for example, the diesel engine 101, the first electric motor102, and the hydraulic pump 103 are mechanically connected so as to runat an identical speed. Hydraulic fluid sent from the hydraulic pump 103is distributed by a control valve 104 based on an operation by theoperator and supplied to the hydraulic cylinders 105, 106 and 107, aleft track hydraulic motor 108, and a right track hydraulic motor 109.The hydraulic cylinder 105 drives the bucket 205 shown in FIG. 1. Thehydraulic cylinder 106 drives the arm 204 shown in FIG. 1. The hydrauliccylinder 107 drives the boom 203 shown in FIG. 1. The left trackhydraulic motor 108 and the right track hydraulic motor 109 drive theleft track structure and the right track structure, respectively, of thetrack structure 201 shown in FIG. 1.

The first electric motor 102 and a second electric motor 112 that drivesthe swing mechanism 113 are each a three-phase synchronous motor and amotor generator. An electric power converter 110 converts direct current(DC) electric power stored in an electric energy storage device 111 tothree-phase alternating current (AC) electric power and supplies thethree-phase AC electric power to, and thereby drive, the first electricmotor 102 and the second electric motor 112. The first electric motor102 is also operated as a generator to charge the electric energystorage device 111 via the electric power converter 110. The secondelectric motor 112 operates as a generator when the swing structure 202rotating is to be braked, thereby charging the electric energy storagedevice 111 via the electric power converter 110.

A capacitor having a relatively small capacity is used for the electricenergy storage device 111. In this case, a charge amount of the electricenergy storage device 111 needs to be appropriately controlled.

A subtractor 120 calculates a difference between a charge amount commandQ* and a charge amount Q of the electric energy storage device 111. Thecharge amount command Q* is given by a host controller and is apredetermined value that corresponds to, for example, an 80% chargeamount of the electric energy storage device 111.

A charge amount control device 114 calculates and outputs a torquetarget so that the difference obtained by the subtractor 120 becomesequal to 0, specifically, the charge amount Q of the electric energystorage device 111 agrees with the charge amount command Q*. A torquelimiter 115 obtains and outputs a first torque command T1* that limits arate of change with time relative to the torque target output by thecharge amount control device 114. If, for example, the torque targetvalue changes in a step fashion, the torque target value is made tochange gradually, so that the rate of change with time in the torquetarget may be limited to a level below a predetermined value.

An engine controller 116 controls the diesel engine 101 so that outputtorque of the diesel engine 101 becomes equal to the first torquecommand T1*. Specifically, the engine controller 116 controls an amountof fuel supplied by a fuel injection valve of the diesel engine 101 to acombustion chamber of the diesel engine 101 or an EGR recirculationamount.

A subtractor 117 calculates a difference between a rotational speedcommand N* and a rotational speed N of the first electric motor. Therotational speed command N* is given by a host controller and is, forexample, a predetermined value.

A speed control device 118 obtains a second torque command T2* based onthe difference calculated by the subtractor 117 so that the rotationalspeed command N* agrees with the rotational speed N of the firstelectric motor and outputs the second torque command T2* to the electricpower converter 110. The electric power converter 110 controls so thattorque of the first electric motor 102 becomes equal to the secondtorque command T2*.

A swing control device 119 obtains a third torque command T3* based onan operating amount of a swing lever operated by the operator andoutputs the third torque command T3* to the electric power converter 110in order to control the second electric motor 112. The electric powerconverter 110 controls so that torque of the second electric motor 112becomes equal to the third torque command T3*.

The electric power converter 110 includes first and second electricpower converting portions built therein, the first electric powerconverting portion controlling the first electric motor 102, the secondelectric power converting portion controlling the second electric motor112. For example, the first electric power converting portion includes aplurality of switching elements and a control part. The switchingelements convert DC electric power to three-phase AC electric power. Thecontrol part performs PWM control for opening or closing the switchingelements so that current flowing through the first electric motor 102agrees with a current command corresponding to the abovementioned secondtorque command T2*. The first electric power converting portion therebycontrols so that the torque of the first electric motor 102 becomesequal to the second torque command T2*. Additionally, when the firstelectric motor 102 operates as a generator, the control part controlsthe switching elements and converts an output of electric powergenerated by the first electric motor 102 to DC electric power andstores the DC electric power in the electric energy storage device 111.The second electric power converting portion, having arrangements andoperations identical to those of the first electric power convertingportion, controls so that the torque of the second electric motor 112becomes equal to the third torque command T3*. When the second electricmotor 112 operates as a generator, the control part controls theswitching elements and converts an output of electric power generated bythe second electric motor 112 to DC electric power and stores the DCelectric power in the electric energy storage device 111.

Operations of the drive system incorporated in the construction machineaccording to the first embodiment will be described below with referenceto FIGS. 3 to 8.

FIGS. 3 to 8 are timing charts showing the operations of the drivesystem incorporated in the construction machine according to the firstembodiment of the present invention.

Operations of different parts of the drive system when, for example, thearm is operated will first be described below with reference to FIG. 3.

The abscissas on FIG. 3 represent elapsed time. The ordinate on FIG. 3(a) represents pump torque of the hydraulic pump 103 and the ordinate onFIG. 3( b) represents the rotational speed N of the first electric motor102. It is assumed that the diesel engine 101, the first electric motor102, and the hydraulic pump 103 are mechanically connected so as to runat an identical speed. The ordinate on FIG. 3( c) represents torque ofthe first electric motor 102 and the ordinate on FIG. 3( d) representsdischarge current of the electric energy storage device 111. Theordinate on FIG. 3( e) represents the charge amount Q of the electricenergy storage device 111 and the ordinate on FIG. 3( f) representstorque of the diesel engine 101. FIG. 3 then shows that torque of thehydraulic pump 103 increases as a result of an operation performed bythe operator at time t1. One of the cases in which the torque of thehydraulic pump 103 increases as a result of an operation of the operatoris when, for example, the operator operates an operating lever for thebucket 205 shown in FIG. 1 and the torque of the hydraulic pump 103 isincreased to drive the hydraulic cylinder 105 according to theoperation. Other possible cases include when each one of the boom 203,the arm 204 or the track structure 201 is driven.

When the torque of the hydraulic pump 103 is increased at time t1 asshown in FIG. 3( a), the rotational speed N decreases as shown in FIG.3( b) with a resultant increase in the difference from the rotationalspeed command N*; this increases the second torque command T2*, whichincreases the torque of the first electric motor 102 as shown in FIG. 3(c). This causes the rotational speed N to start increasing and torecover at time t2 as shown in FIG. 3( b). Specifically, even withfluctuations in pump torque, the speed control device 118 controls thetorque of the first electric motor 102 and the rotational speed N ismaintained at a constant level.

When the torque of the first electric motor 102 is increased at time t1as shown in FIG. 3( c), the discharge current of the electric energystorage device 111 increases at time t1 to supply electric power asshown in FIG. 3( d) and the charge amount Q decreases as shown in FIG.3( e). This increases the difference from the charge amount command Q*calculated by the subtractor 120, which increases the engine torquetarget output by the charge amount control device 114. The torque targetis subject to limitation of the rate of change with time imposed by thetorque limiter 115 and output as the first torque command T1* to theengine controller 116. FIG. 3( f) shows the diesel engine torque whenthe rate of change with time in the first torque command T1* is limitedas described above. Changes in torque after time t1 follow the rate ofchange with time limited by the torque limiter 115 or lower. Thiseliminates the likelihood that the diesel engine 101 will change itstorque sharply and allows the diesel engine 101 to avoid combustion in acondition of high equivalence ratios due to excessive fuel injectionwith which particulate matter tends to be produced or in a condition ofexcessive combustion temperatures at which nitrogen oxide tends to beproduced.

When the torque of the diesel engine 101 increases at time t2 to time t3as shown in FIG. 3( f), the torque of the first electric motor 102decreases in proportion thereto as shown in FIG. 3( c). This is becauseof the torque of the first electric motor 102 being controlled so that asum of the torque of the diesel engine 101 and the torque of the firstelectric motor 102 balances the pump torque to thereby keep therotational speed N constant.

The control at time t2 to time t3 will be described in greater detailbelow. Because the charge amount Q of the electric energy storage device111 decreases at time t2, the difference output by the subtractor 120increases. Accordingly, the torque target value output by the chargeamount control device 114 increases. The engine controller 116 controlsthe output torque of the diesel engine 101 according to the torquetarget value, which causes the torque of the diesel engine 101 toincrease gradually as shown in FIG. 3( f). Meanwhile, when the outputtorque of the diesel engine 101 increases, the rotational speed of thediesel engine 101 increases and the rotational speed of the firstelectric motor 101 connected to the diesel engine 101 also increases. Asa result, the speed difference output by the subtractor 117 increases.This causes the second torque command T2* output by the speed controldevice 118 to decrease. The torque of the first electric motor 101,being controlled by the electric power converter 110 according to thesecond torque command T2*, gradually decreases as shown in FIG. 3( c).

When the torque of the diesel engine 101 exceeds the pump torque at timet3, the torque of the first electric motor 102 becomes negative,specifically, the first electric motor 102 performs an electric powergenerating operation and the diesel engine 101 drives the first electricmotor 102 that performs the electric power generating operation as wellas the hydraulic pump 103. In addition, the electric power generated bythe first electric motor 102 is supplied to the electric energy storagedevice 111, which causes the charge amount Q to start increasing towardthe charge amount command Q* as shown in FIG. 3( e).

At time t4, the charge amount Q shown in FIG. 3( e) substantially agreeswith the charge amount command Q*. At this time, the torque of the firstelectric motor 102 is 0 as shown in FIG. 3( c) and the torque of thediesel engine 101 balances the pump torque with the rotational speed Ncontrolled at the rotational speed command N*.

Operations of different parts of the drive system when the swingstructure 202 performs a swing operation will be described below withreference to FIG. 4. The ordinates on FIGS. 4( a) to 4(f) represent thesame as those on FIGS. 3( a) to 3(f). FIG. 4( g) shows the output of thesecond electric motor 112. FIG. 4 shows that the second electric motor112 is started by an operation of the swing lever performed by theoperator at time t1, the second electric motor 112 is braked by anoperation of the swing lever performed by the operator at time t2, andthe second electric motor 112 is brought to a stop at time t4.

When the second electric motor 112 starts rotating at time t1, therotational speed starts increasing, which increases the output of thesecond electric motor 112 as shown in FIG. 4( g). Accordingly, toprevent the charge amount Q of the electric energy storage device 111from being decreased due to an increase in the discharge current of theelectric energy storage device 111, the torque target output by thecharge amount control device 114 increases. This increases the torque ofthe diesel engine 101 as shown in FIG. 4( f). Meanwhile, to prevent therotational speed N from increasing due to the increase in the torque ofthe diesel engine 101, the speed control device 118 decreases the secondtorque command T2*. This makes the torque of the first electric motor102 negative as shown in FIG. 4( c). The first electric motor 102 thenperforms the electric power generating operation and the dischargecurrent of the electric energy storage device 111 is prevented fromincreasing, so that the charge amount Q can be prevented fromdecreasing. Specifically, the torque of the diesel engine 101 increasesin proportion to the output of the second electric motor 112. The firstelectric motor 102 then generates electric power with the increasedtorque, so that the rotational speed N and the charge amount Q arecontrolled so as to agree with the rotational speed command N* and thecharge amount command Q*, respectively. It is noted that the rate ofchange with time in the torque target associated with the increase inthe output of the second electric motor 112 at this time is equal to, orlower than, the limited value and the first torque command T1* agreeswith the torque target.

Through the foregoing control, at time t1 to time t2, the torque of thediesel engine 101 increases as shown in FIG. 4( f) and the torque of thefirst electric motor 102 decreases (the amount of electric powergenerated increases) as shown in FIG. 4( c), in proportion to theincrease in the output of the second electric motor 112 as shown in FIG.4( g).

When deceleration of the second electric motor 112 is started at timet2, the output suddenly changes from powering to regeneration. Theoutput of the second electric motor 112 undergoes a sudden change frompositive to negative as shown in FIG. 4( g). Accordingly, in order toabsorb electric power regenerated by the second electric motor 112 andelectric power generated by the first electric motor 102, the dischargecurrent of the electric energy storage device 111 is decreased as shownin FIG. 4( d), specifically, charging of the electric energy storagedevice 111 is started as shown in FIG. 4( e) to increase the chargeamount Q. As the charge amount Q increases, the torque target isdecreased by the charge amount control device 114. At this time, thetorque target tends to change sharply because of the precipitous changein the output of the second electric motor 112; however, because of therate of change in the first torque command T1* being limited by thetorque limiter 115, the torque of the diesel engine 101 does not changeprecipitously, as shown in FIG. 4( f).

This prevents the diesel engine 101 from changing its torqueprecipitously and allows the diesel engine 101 to avoid combustion in acondition of high equivalence ratios due to excessive fuel injectionwith which particulate matter tends to be produced or in a condition ofexcessive combustion temperatures at which nitrogen oxide tends to beproduced.

The torque of the first electric motor 102 with its rotational speed Ncontrolled at a constant level increases with the deceasing torque ofthe diesel engine 101 as shown in FIG. 4( c) and the amount of electricpower generated by the first electric motor 102 decreases slowly. Thus,the charge amount Q continues to increase for some while.

The torque of the first electric motor 102 continues to increase and thefirst electric motor 102 shifts from an electric power generating stateto a powering state. Then, when power consumption exceeds the electricpower regenerated by the second electric motor 112 at time t3, thecharge amount Q starts decreasing as shown in FIG. 4( e). When thecharge amount Q decreases, the torque target is increased by the chargeamount control device 114 and, as shown in FIG. 4( f), the torque of thediesel engine 101 increases. To prevent the rotational speed N fromincreasing due to the increase in the torque of the diesel engine 101,the speed control device 118 decreases the torque of the first electricmotor 102 and the discharge current of the electric energy storagedevice 111 decreases as shown in FIG. 4( c).

As a result, the following conditions develop at time t5: specifically,the torque of the first electric motor 102 is 0 as shown in FIG. 4( c),the discharge current of the electric energy storage device 111 is 0 asshown in FIG. 4( d), the charge amount Q agrees with the charge amountcommand Q* as shown in FIG. 4( e), and the torque of the diesel engine101 agrees with the pump torque.

As described above, even when the second electric motor 112 performspowering and regenerative operations as a result of a swing operation,the rotational speed N is controlled so as to agree with the rotationalspeed command N*, the rate of change with time in the torque of thediesel engine 101 can be limited, and the charge amount Q of theelectric energy storage device 111 is controlled so as to agree with thecharge amount command Q*.

Changes with time of the pump torque, the rotational speed N, the torqueof the first electric motor 102, and the torque of the diesel engine 101when the rate of change with time in the pump torque is changed will bedescribed below with reference to FIGS. 5 to 8.

FIGS. 5 to 8 are each concerned with a specific condition of the rate ofchange with time in the pump torque, the conditions being labeled ascondition 1 to condition 4. Conditions 1 and 2 show cases with low ratesof change with time in the pump torque and conditions 3 and 4 show caseswith high rates of change with time in the pump torque. Conditions 2 and4 are concerned with rates of change with time in the pump torque twiceas high as those of conditions 1 and 3, respectively.

The abscissas on FIGS. 5 to 8 represent time. The ordinate on FIG. 5( a)represents the pump torque of the hydraulic pump 103 and the ordinate onFIG. 5( b) represents the rotational speed N of the first electric motor102. It is assumed that the diesel engine 101, the first electric motor102, and the hydraulic pump 103 are mechanically connected so as to runat an identical speed. The ordinate on FIG. 5( c) represents the torqueof the first electric motor 102 and the ordinate on FIG. 5( f)represents the torque of the diesel engine 101. The broad dotted line onFIG. 5( f) is a reference line that serves as a guide easily determiningan inclination of a torque line. The ordinates on FIGS. 6( a) to 6(c)and 6(f) to FIGS. 8( a) to 8(c) and 8(f) represent the same as thoserepresented by the ordinates on FIGS. 5( a) to 5(c) and 5(f).

In condition 1 (FIG. 5) and condition 2 (FIG. 6), because of the lowrates of change with time in the pump torque as shown in FIGS. 5( a) and6(a), the torque of the diesel engine 101 can follow the increase in thepump torque as shown in FIGS. 5( f) and 6(f). This eliminates the needfor making the torque of the first electric motor 102 large and, asshown in FIGS. 5( c) and 6(c) and the torque of the first electric motor102 is smaller than the torque of the diesel engine 101 at the peak ofthe torque of the first electric motor 102.

In contrast, in condition 3 (FIG. 7) and condition 4 (FIG. 8), becauseof the high rates of change with time in the pump torque as shown inFIGS. 7( a) and 8(a), the torque of the diesel engine 101 cannot followthe increase in the pump torque. To maintain the rotational speed N, thetorque of the first electric motor 102 needs to be made large as shownin FIGS. 7( c) and 8(c) and becomes larger than the torque of the dieselengine 101 at the peak of the torque of the first electric motor 102.

Attention is now focused on the rate of change with time in the pumptorque of the diesel engine 101 when the rate of change with time in thepump torque changes from condition 1 to condition 2 in conditions 1 and2 having the low rates of change with time in the pump torque. The rateof change with time in the torque of the diesel engine 101 in condition2 (FIG. 6) changes greatly relative to that in condition 1 (FIG. 5). Incontrast, in conditions 3 and 4 having the low rates of change with timein the pump torque, because of the limitation imposed by the torquelimiter 115, the rate of change with time in the torque of the dieselengine 101 in condition 4 (FIG. 8) changes a little relative to that incondition 3 (FIG. 7) when the rate of change with time in the pumptorque changes from condition 3 to condition 4. Specifically, when therates of change with time in the pump torque are low (conditions 1 and2), the increase in the rate of change with time in the torque of thediesel engine 101 relative to the increase in the rate of change withtime in the pump torque is high; and when the rates of change with timein the pump torque are high (conditions 3 and 4), the increase in therate of change with time in the torque of the diesel engine 101 relativeto the increase in the rate of change with time in the pump torque islow.

In either case, because of the functioning of the speed control device116, the rotational speed N is controlled so as to agree with therotational speed command N*. Specifically, in the construction machineaccording to the first embodiment, the torque of the diesel engine 101is controlled according to the pump torque when the rate of change withtime in the pump torque is low; because the rate of change with time inthe torque of the diesel engine 101 is low at this time, the dieselengine 101 does not develop a condition in which particulate matter andnitrogen oxide tend to be produced.

In contrast, when the rate of change with time in the pump torque ishigh, the rate of change with time in the torque of the diesel engine101 is limited and is not controlled according to the pump torque. Thus,in this case, too, the rate of change with time in the torque of thediesel engine 101 is limited, so that the diesel engine 101 does notdevelop a condition in which particulate matter and nitrogen oxide tendto be produced.

As described heretofore, in the first embodiment, the particulate matter(PM) or the nitrogen oxide (NOx) discharged from the internal combustionengine mounted on the construction machine can be reduced and the chargeamount of the electric energy storage device that supplies electricpower to the electric motor can be appropriately controlled.

Additionally, the charge amount of a capacitor having a small capacity,if used for the electric energy storage device, can also beappropriately controlled.

Arrangements and operations of a construction machine according to asecond embodiment of the present invention will be described below withreference to FIGS. 9 to 11. A hydraulic excavator as the constructionmachine according to the second embodiment has a general arrangementidentical to that shown in FIG. 1.

An arrangement of a drive system that drives the construction machineaccording to the second embodiment will be described below withreference to FIG. 9.

FIG. 9 is a block diagram showing the arrangement of the drive systemthat drives the construction machine according to the second embodimentof the present invention. Like or equal parts are identified by the samereference numerals as those used in FIG. 2.

Based on a difference between a rotational speed command N* and arotational speed N′ of a diesel engine 101 obtained by a subtractor 130,a second speed control device 131 calculates a torque target such thatthe rotational speed N′ of the diesel engine 101 agrees with therotational speed command N*. The second speed control device 131 thenoutputs the torque target to a torque limiter 115.

A high-pass filter 132 produces an output of a speed control device 118from which a low-frequency component including a DC component isremoved. A subtractor 133 subtracts an output of a charge amount controldevice 114 from the output of the high-pass filter 132 representing theoutput of the speed control device 118 from which the low-frequencycomponent including the DC component is removed. The subtractor 133 thenoutputs the result as a second torque command T2*.

It is noted that the diesel engine 101 and a first electric motor 102are mechanically connected to each other and thus run at an identicalspeed that will hereinafter be represented by a rotational speed N.

Operations of the drive system according to the second embodiment willbe described below.

When torque of a hydraulic pump 103 changes, the second speed controldevice 131 limits fluctuations in the rotational speed N; still, thetorque limiter 115 limits the rate of change in torque of the dieselengine 101. This prevents the diesel engine 101 from developing acondition in which particulate matter or nitrogen oxide tends to beproduced. Meanwhile, because of the rate of change in the torque of thediesel engine 101 being limited, it is difficult to sufficiently limitthe fluctuations in the rotational speed N only with the second speedcontrol device 131. Thus, the fluctuations in the rotational speed N islimited transiently by the speed control device 118. In addition,because the low-frequency component is removed by the high-pass filter132 in a steady state, control of the charge amount Q by the chargeamount control device 114 is performed.

Operations of the drive system incorporated in the construction machineaccording to the second embodiment will be described below withreference to FIGS. 10 to 11.

FIGS. 10 and 11 are timing charts showing operations of the drive systemincorporated in the construction machine according to the secondembodiment of the present invention.

FIG. 10 shows operations of different parts of the drive system when,for example, the arm is operated and the pump torque is changed. Theoperations are the same as those described with reference to FIG. 3.

In this case, the rotational speed N is controlled so as to agree withthe rotational speed command N*, the rate of change with time in thetorque of the diesel engine 101 is limited, and the charge amount Q ofan electric energy storage device 111 is controlled so as to agree withthe charge amount command Q*.

FIG. 11 shows operations of different parts of the drive system when asecond electric motor 112 is operated. The operations are the same asthose described with reference to FIG. 4.

In this case, the rotational speed N is controlled so as to agree withthe rotational speed command N*, the rate of change with time in thetorque of the diesel engine 101 is limited, and the charge amount Q ofthe electric energy storage device 111 is controlled so as to agree withthe charge amount command Q*.

As described heretofore, in the second embodiment, too, the particulatematter (PM) or the nitrogen oxide (NOx) discharged from the internalcombustion engine mounted on the construction machine can be reduced andthe charge amount of the electric energy storage device that supplieselectric power to the electric motor can be appropriately controlled.

Additionally, the charge amount of a capacitor having a small capacity,if used for the electric energy storage device, can also beappropriately controlled.

In the above-described embodiments, a predetermined constant value isgiven as the rotational speed command N*. The rotational speed commandN* may, however, be decreased for a light hydraulic pump load orincreased for a heavy hydraulic pump load. Varying the rotational speedcommand N* in this manner still allows the rotational speed N to followthe rotational speed command N* because of the control performed basedon the difference therebetween.

The rate of change with time of the torque limiter 105, while it hasbeen described to be constant, may still be varied depending on theoperating condition of the diesel engine 101 within a range in which theparticulate matter or the nitrogen oxide does not increase to a levelmore than a predetermined amount. Additionally, an input to, and anoutput from, the torque limiter 105 are made to agree with each othersuch that the particulate matter or the nitrogen oxide does not increaseto a level more than a predetermined amount and the torque limiter 105may be configured so as to limit the rate of change with time in theoutput if the particulate matter or the nitrogen oxide increases to alevel more than the predetermined amount with the input made to agreewith the output.

Additionally, the diesel engine 101, the first electric motor 102, andthe hydraulic pump 103 are mechanically connected so as to run at anidentical speed. The connection may nonetheless be achieved via atransmission, in which case, the rotational speed command N*, therotational speed N′, and the rotational speed N need to be converted inconsideration of a gear ratio.

DESCRIPTION OF REFERENCE NUMERALS

-   101 Diesel engine (internal combustion engine)-   102 First electric motor-   103 Hydraulic pump (hydraulic pressure generator)-   104 Control valve-   105, 106, 107 Hydraulic cylinder-   108, 109 Hydraulic motor-   110 Electric power converter-   111 Electric energy storage device-   112 Second electric motor-   113 Swing mechanism-   114 Charge amount control device-   115 Torque limiter (second control means)-   116 Engine controller-   118 Speed control device (first control means)-   119 Swing control device-   131 Second speed control device-   132 High-pass filter-   200 Hydraulic excavator (exemplary construction machine)

1. A construction machine including an internal combustion enginecontrolled based on a torque command, an electric motor mechanicallyconnected to the internal combustion engine, an electric energy storagedevice that supplies electric power to the electric motor, and ahydraulic pressure generator, the construction machine performing workby driving the hydraulic pressure generator using the internalcombustion engine and the electric motor, the construction machinecomprising: first control means that controls a speed of the electricmotor based on a speed command; and second control means that obtainsthe torque command having a rate of change with time limited based on atorque target.
 2. The construction machine according to claim 1, whereinthe internal combustion engine is controlled by a first torque commandobtained based on the speed command and the speed of the internalcombustion engine, and the first control means calculates a secondtorque command obtained based on the speed command and the speed of theelectric motor, further includes a high-pass filter that removes alow-frequency component including a DC component of the second torquecommand, and controls the electric motor based on an output of thehigh-pass filter.
 3. The construction machine according to claim 1,wherein the electric motor is speed-controlled by the speed command, andtorque of the internal combustion engine is greater than torque of theelectric motor when a rate of change with time in torque of thehydraulic pressure generator is low, and the torque of the electricmotor is greater than the torque of the internal combustion engine whenthe rate of change with time in the torque of the hydraulic pressuregenerator is high.
 4. The construction machine according to claim 1,wherein the electric motor is speed-controlled by the speed command, anda change of a rate of change with time in the torque of the internalcombustion engine is higher than a change of a rate of change with timein the torque of the hydraulic pressure generator when the rate ofchange with time in the torque of the hydraulic pressure generator islow, and the change of the rate of change with time in the torque of theinternal combustion engine is lower than the change of the rate ofchange with time in the torque of the hydraulic pressure generator whenthe rate of change with time in the torque of the hydraulic pressuregenerator is high.
 5. The construction machine according to claim 1,wherein the torque target is obtained based on a charge amount of theelectric energy storage device.
 6. A construction machine comprising: aninternal combustion engine; an electric motor mechanically connected tothe internal combustion engine; an electric energy storage device thatsupplies electric power to the electric motor and a hydraulic pressuregenerator; the construction machine performing work by driving thehydraulic pressure generator using the internal combustion engine andthe electric motor; wherein the electric motor is speed-controlled by aspeed command; and torque of the internal combustion engine is greaterthan torque of the electric motor when a rate of change with time intorque of the hydraulic pressure generator is low; and the torque of theelectric motor is greater than the torque of the internal combustionengine when the rate of change with time in the torque of the hydraulicpressure generator is high.
 7. A construction machine comprising: aninternal combustion engine; an electric motor mechanically connected tothe internal combustion engine; an electric energy storage device thatsupplies electric power to the electric motor and a hydraulic pressuregenerator; the construction machine performing work by driving thehydraulic pressure generator using the internal combustion engine andthe electric motor; wherein the electric motor is speed-controlled bythe speed command; and a change of a rate of change with time in torqueof the internal combustion engine is higher than a change of a rate ofchange with time in torque of the hydraulic pressure generator when therate of change with time in the torque of the hydraulic pressuregenerator is low; and the change of the rate of change with time in thetorque of the internal combustion engine is lower than the change of therate of change with time in the torque of the hydraulic pressuregenerator when the rate of change with time in the torque of thehydraulic pressure generator is high.